The primary purpose of this research is to search in nonhuman primates for possible models of ccnditions associated with aging in human beings. There will be three projects: 1) We will evaluate the frequency of occurrence in nonhuman primates of benign prostatic hyperplasia and conduct a study of its morphologic, endocrine and other biochemical characteristics. 2) We will study the influence of cerebral altherosclerosis on cerebral blood flow, learning and memory, and morphologic characteristics of brain in monkeys with atherosclerosis and/or hypertension. An attempt to obtain comparable data on human subjects will be made. 3) Sexual behavior of male nonhuman primates with severe atherosclerosis will be evaluated in combination with measurement of gonadal steroids. At necropsy, the pelvic and genital blood vessels will be carefully examined.